1. Field of the Invention
This invention relates to a coated abrasive article and a method of making the coated abrasive article, and in particular to a method wherein the make coat precursor is at least partially cured before the abrasive grains are applied.
2. Description of the Related Art
Coated abrasives generally comprise a flexible backing upon which a binder holds and supports a coating of abrasive grains. The coated abrasive typically employs a "make" coat precursor of resinous binder material. The make coat secures the abrasive grains to the backing. A "size" coat precursor of resinous binder material is applied over the make coat and abrasive grains. The size coat firmly bonds the abrasive grains to the backing. Additionally, the abrasive grains are generally oriented with their longest dimension perpendicular to the backing to provide an optimum cut rate.
In a typical manufacturing process for making coated abrasives, the make coat precursor is first applied to the backing. This is followed by electrostatic projection of the abrasive grains into the make coat precursor. The make coat precursor is then partially cured in order to set the abrasive grains. Next, the size coat precursor is applied over the abrasive grains. Finally, the make coat precursor and size coat precursor are fully cured.
One of the major problems associated with this process, is the tendency to apply multiple layers of abrasive grains during the electrostatic coating. This is particularly true in the "fine" grades, that is, where the average particle size of the abrasive grain is less than about 150 micrometers, and usually less than about 100 micrometers. In some instances there may be up to seven layers of abrasive grains applied. This multiple layer becomes increasingly a problem as the abrasive grain particle size is decreased. Reducing the coating weight of the abrasive grain tends to result in a blotchy, non-uniform type coating of multiple layers.
There are a number of disadvantages associated with the multiple layers of abrasive grains. The abrasive grains tend not to be ideally oriented and the abrasive grains tend to lay on top of one another. This results in reduced abrading performance. The multiple layers of abrasive grains can in some cases, reduce the flexibility of the product. Furthermore, the multiple layers of abrasive grains decrease cost efficiency of the coated abrasive due to the extra layers of abrasive grains.
U.S. Pat. No. 2,015,658 (Bezzenberger) describes a method to avoid multiple layer phenomena when forming abrasive articles. The abrasive grain is applied to the make coat precursor by means of a metered roll.
U.S. Pat. No. 2,053,360 (Benner et al.) describes a method of making a coated abrasive wherein the abrasive grains are sprinkled onto a nontacky film of a plasticizable binder. The film is then plasticized such that the binder wets the surface of the abrasive grain.
U.S. Pat. No. 4,047,903 (Hesse et al.) describes a radiation curable binder comprising a resin prepared by at least a partial reaction of (a) epoxy monomers having at least 2 epoxy groups, for example, from diphenylolpropane and epichlorohydrin, with (b) unsaturated monocarboxylic acids, and (c) optionally, polycarboxylic acid anhydride.
U.S. Pat. No. 4,588,419 (Caul et al.) describes an adhesive for coated abrasives comprising a mixture of (a) an electron beam radiation curable resin system comprising an oligomer selected from the group consisting of urethane acrylates and epoxy acrylates, a filler and a diluent, and (b) a thermally curable resin selected from the group consisting of phenolic resins, melamine resins, amino resins, alkyd resins, and furan resins.
U.S. Pat. No. 4,751,138 (Tumey et al.) describes a coated abrasive in which either the make coat or the size coat comprises an ethylenically unsaturated compound, an epoxy monomer and a photoinitiator.
U.S. Pat. No. 4,927,431 (Buchanan et al.) describes an adhesive for coated abrasives comprising a mixture of (a) a radiation curable monomer selected from the group consisting of isocyanurate derivatives having at least one terminal or pendant acrylate group, isocyanate derivatives having at least one terminal or pendant acrylate group, and multifunctional acrylates having on average at least three pendant acrylate groups, and (b) a thermally curable resin selected from the group consisting of phenolic resins, epoxy monomers, urea-formaldehyde resins, melamine-formaldehyde resins, and polyamide resins.
U.S. Pat. 4,985,340 (Palazzotto et al.) describes a polymeric precursor that can be employed as a binder for abrasive articles. The polymeric precursor is selected from the group consisting of (1) at least one ethylenically unsaturated monomer, optionally, in combination with an epoxy monomer or polyurethane precursor, (2) at least one epoxy monomer, or (3) polyurethane precursors, and a curing agent comprising an organometallic salt and an onium salt.
U.S. Pat. No. 4,997,717(Rembold) describes a process for preparing a coated abrasive by applying a binder layer to a support, briefly irradiating the binder layer with actinic light, and then applying abrasive grain to the still tacky layer before or after irradiation, and subsequent or simultaneous heat curing.